The present invention relates generally to optical transceiver modules, and more particularly to optical transceiver modules employing a receiver and a transmitter having a laser operating in conjunction with a controller to provide improved laser initialization performance.
The use of fiber optics technology in data communication continues to expand at a rapid pace. Optic fiber transmission links are used widely in connecting computer, telephone, and instrumentation systems. Fiber optic systems have tremendous advantages over systems utilizing copper conductors. Besides being smaller and lighter than copper conductor systems, fiber optic systems offer total electrical isolation, extremely high-speed wideband capability, and complete immunity to both noise and the broad spectrum of interference. Most importantly, fiber optic communication links are much less expensive than copper conductor systems.
A basic fiber optic communication link has three components: a transmitter, a receiver, and a fiber optic cable. The transmitter contains a light-emitting element that converts an electrical current into an optical signal. The light emitting diode is typically a light-emitting diode, a laser diode, or a vertical cavity surface-emitting laser. The receiver contains a light-detecting element that converts the light signal back into an electrical current. The fiber optic cable connects the transmitter to the receiver and carries the optical signal between them.
More commonly, however, a fiber optic link comprises a pair of optical transceivers coupled by a pair of fiber optic cables. An optical transceiver combines a transmitter with a receiver to form a single unit that provides all required electrical/optical conversions necessary to both transmit and receive optical data. The transmitter of the first transceiver sends data in the form of an optical signal via one of the fiber optic cables to the receiver of the second transmitter which subsequently converts the optical signal to an electrical signal. Likewise, the transmitter of the second transceiver sends an optical signal via the other fiber optic cable to the receiver of the first transceiver.
In an optical transceiver module utilizing a laser as the light emitting element, one critical task which must be performed quickly and accurately in order to provide a quality product is initializing, or starting, the laser. Each time the laser is powered-up, its optical output power level must be brought up and stabilized within a desired range, or window, for safe operation. The laser""s optical output power level is controlled by adjusting a bias current provided to the laser. Laser initialization generally occurs each time the optical transceiver module is turned on, or after some type of transceiver fault or disable has been negated. Rapid start-up of the laser is desirable to place the transceiver into operation as quickly as possible.
Historically, optical transceiver modules have been constructed as xe2x80x9chard-codedxe2x80x9d integrated circuits (IC""s). In other words, individual circuits comprising a plurality of transistors are designed into the IC with each circuit dedicated to carrying out a single task related to the control and operation of the transceiver. Common practice now is to store a manufacturing target for the laser power in a circuit dedicated to initializing the laser. If the actual optical output power is too low at start-up, the circuit increments the bias current. Likewise, if the optical output power is too high, the circuit decrements the bias current. A major disadvantage of this approach is that several iterations are sometimes required to bring the laser output power within the desired window, which delays the ability of the optical transceiver to begin transmitting optical data.
Optical data systems would benefit from an optical transceiver module than can more quickly and more accurately bring the optical output power of a laser to a value within a desired operating window upon initialization.
One aspect of the present invention provides an optical transceiver module including a laser and a controller. The laser is configured to provide an optical output signal having a power level that is based on a bias current. The controller is configured to cause the laser to be biased with an initial bias current, to receive a monitoring signal indicative of the power level, to compare the power level to a desired power level range, and to cause the laser to be biased with an adjusted bias current if the power level is not within the desired power level range.